Method of reducing tubes,especially thick-walled tubes and means for practicing the method



Feb. 17 19 70 a; K. MULLER I 3,

, METHOD OF REDUCING TUBES ESPECIALLY THICK-WALLED TUBES AND MEANS FOR :PRAGTICING THE METHOD Filed Jun; 13,1967 I m INVENTORZ GERHARD KARL GUNTHER MULLER;

United States Patent 3,495,429 METHOD OF REDUCING TUBES, ESPECIALLY THICK-WALLED TUBES AND MEANS FOR PRACTICING THE METHOD Gerhard Karl Giinther Miiller, Hofors, Sweden, assignor to Aktiebolaget Svenska Kullagerfahriken, Goteborg, Sweden, a corporation of Sweden Filed June 13, 1967, Ser. No. 645,717 Claims priority, application Sweden, June 16, 19.66, 8,260/ 66 Int. Cl. B21b 19/06 U.S. Cl. 72-100 1 Claim ABSTRACT OF THE DISCLOSURE A tube reducing mill comprising a plurality of rolls wherein the tube outer diameter is reduced without appreciably changing the thickness of the wall, each roll having a central rotational axis disposed at an angle relative to the tube axis and having at least three zones, namely, a feeding zone, a reducing zone and a smoothing zone. The feeding zone and smoothing zone are defined by frusto-conical circumferentially extending surfaces separated by a shoulder defining a reducing zone. The surface of the reducing zone is inclined relative to the axis of the tube at a predetermined angle so that the outer diameter of the tube may be reduced between 5%-31% during passage of the tube through the mill.

The present invention relates to a method and means for the reduction of primarily thick-walled tubes in which the wall thickness is maintained practically constant. The purpose of the invention is to eliminate certain disadvantages arising in this process in conventional rolling mills and to make it possible to manufacture tubes with comparatively greater wall thickness than has hitherto been possible.

Tube reducing mills of hitherto known types for reducing the outer diameter while maintaining the wall thickness comprise a plurality of rolling mill stands with two or more rolls which work on the tube in an axial direction. The rolls of subsequent stands are frequently disposed at a suitable angle relative to those of the preceding stand, the grooves of following rolls being smaller than those of the preceding rolls.

In this type of tube reducing mill considerable difficulty is often encountered in reducing tubes in which the relationship of the outer diameter to wall thickness (Odzw) is less than 6 and the reduction of the outer diameter greater than 10% because of the difiiculty of preventing the flow of metal in other directions than those desired with the result that the bores of the tubes will be more or less quadrilateral or hexagonal and the wall thickness will vary along the length of the tube.

Another way of reducing a tube is by the well-known Assel method. According to this principle the rolling takes place in a direction practically perpendicular to the axis of the rotating tube, which is fed forward while being rotated past three substantially conical rolls having shoulders on their rolling surfaces. The work of reduction is concentrated at the shoulders thereby that the material is worked upon between a mandrel applied in the tube and the shoulders of the rolls. A substantial reduction of the wall thickness can be obtained when rolling according to this principle. For practical reasons the Assel method cannot be used when the relationship Odzw of the finished tube is less than 4.5.

It has also been proposed to calibrate the tube by a cross-rolling operation without the use of a mandrel in the tube. It has not, however, been possible to obtain any considerable amount of reduction by this method and its use has mainly been confined to provide an attractive surface on the tube.

As mentioned above, the present invention relates to a method for reducing the inner and outer diameters of the tube without any appreciable change in the wall thickness. The tube is reduced in a three roll tube reducing mill of a design known per se and without the use of a mandrel. According to the invention, however, the rolls differ from those previously known whereby it is made possible to accomplish a considerable reduction of comparatively thick-walled tubes which has hitherto not been possible in rolling mills of known type.

The invention is described in the following with reference to the accompanying drawing in which one of the three rolls of the rolling mill is shown in engagement with the tube to be reduced. As shown the axis of the roll is slightly inclined relative to that of the tube, but it should also be understood that the roll is also inclined sideways relative to the tube.

In the drawing the numeral 1 indicates the tube being rolled and 2 is the roll. The roll profile is divided into four zones, of which the first, at the side at which the the tube enters, is a feeding zone 3 which is comparatively wide. This zone has the form of a truncated cone having a top angle of 6-10. The function of this zone is to grip the tube and through friction rotate it about its axis and feed it into the rolling mill. The angle of inclination at indicated between the lines C and D is preferably about 3-5". The next portion of the profile of the roll is the reducing zone 4 formed by a shoulder on the roll. It consists of a conical rolling surface which is short compared to the other Zones of the roll and straight but slightly rounded where it melts the adjacent zones and has a substantial inclination relative to the axis of the the tube forming an angle ,3 therewith in excess of 40 as indicated by the lines A and B. Under certain circumstances this angle may be a right angle. This angle together with the height of the shoulder where D is the outer diameter of the shoulder (roll diameter) and D, the greatest diameter of the feeding zone of the roll and the shoulder diameter determines the limits of the reduction which it is possible to attain.

In the above mentioned known forms on the contrary the feeding zone of the roll has been made with a very small angle of inclination with the result that only the outer surface of the tube is adjusted during the calibrating operation. In order to obtain good results with the method according to the invention it has been found suitable to make the relationship between the shoulder diameter of the roll and the outer diameter of the tube less than 3.5. With the new method it is possible to reduce the outer diameter of the tube by 5 to 31% with only a comparatively small change in the thickness of the wall. The free Working of the tube in the radial direction between the three rolls causes a flow of material in both radial and axial directions.

Following the reducing zone is a smoothing zone 5 which is nearly parallel with, or inclined not more than 2 relative to, the axis of the tube when the roll engages the tube and converges towards the entrance in-feed end of the mill. The function of this zone is to smooth out irregularities in the surface of the tube. The last zone 6 of the roll is for eliminating out of roundness. The surface of this zone can be either cylindrical or conical with a top angle of 0 to 2". The edges of the outer zones of the rolls may suitably be made convex or have a suitable radius as shown at 7' and 8. In some cases it may be found preferable to combine the smoothing zone and the zone for eliminating out of roundness to form a single zone.

The following advantages are obtained when rolling tubes according to the method of the invention as compared with rolling in conventional tube reducing mills:

(1) A tube is produced having narrow tolerances and uniform wall thickness along its whole length.

(2) All tendency to produce out of round tubes, tubes having quadrilateral bores or other deviations from the ideal form can be easily avoided.

(3) Tubes in which the relationship Odzw is less than 4.5 and in some cases down to 3.0 can be conveniently made.

(4) The mill can be much more easily adjusted to size than conventional mills which means a saving in time when changing over from one dimension to another.

(5) Because of the greater degree of reduction obtainable with the mill according to the invention it can produce longer tubes from the same piercing mill than is possible with conventional mills which results in increased production of the kind of tube being produced.

The invention is in no way limited to the forms described above, but may be varied in different ways within the scope of the following claims. The method may be used for making tubes of metal or other material either in cold or hot state. In the latter case, the reducing operation should suitably take place at a temperature over 700 C.

While a particular embodiment of the present invention has been illustrated and described herein, it is to be understood that changes and modifications may be made within the scope of the following claim.

I claim:

.1. A reducing mill for reducing the outer diameter of a tube without appreciably reducing the thickness of the wall thereof, consisting of a plurality of rotatable working rolls arranged to engage and support the workpiece without the need of a mandrel, means for rotating the working rolls to rotate the tube about its axis and feed the same in longitudinal feed direction relative to the rolls, each roll comprising at least three zones, 2. feeding zone in the form of a truncated cone having a top angle of between 6 and 10, the smaller diameter end of said truncated cone facing in a direction opposite the feed direction of said tube, a reducing zone defined by a conical shoulder and being at an inclination relative to the axis of the tube to form an angle of more than and a smoothing zone defined by a frusto-conical surface inclined not more than 2 relative to the axis of the tube, the relationship between the maximum diameter of the shoulder andthe outer diameter of the tube being less than 3.5, the central axis of said roll being disposed at an angle in the range of 3-5 relative to the axis of the tube,

and a last zone for eliminating out-of-roundness defined by the slightly rounded large terminal end of said roll.

References Cited UNITED STATES PATENTS 2,060,767 11/1936 Assel 72-100 2,101,357 12/1937 Assel 72-100 2,176,412 10/1939 Assel 72l00 2,358,307 9/1944 Dewey 72-100 RICHARD J. HERBST, Primary Examiner 

